The research focus of the Unit on Molecular Virology has been directed towards developing and understanding of the viral and cellular factors involved in the process of retroviral infection. The interaction between the envelope component of the retrovirus and a cell surface protein or receptor on the target cells initiates the infection process. The envelope protein of the retrovirus binds to the receptor and then fuses with the cell membrane. Identification and cloning of the human cDNAs encoding the receptors for the amphotropic murine leukemia viruses (A-MuLVs) and the gibbon ape leukemia viruses (GaLVs) has initiated experimental examination of how these receptors interact with their respective viruses. We have found that substitution of a glutamic acid for the lysine residue at position 522 within the receptor for A-MuLVs is sufficient to convert this receptor to a receptor capable of facilitating only A0MuLV but GaLV entry as well.